The present invention is concerned with, but is not limited to, viewing chambers which require isothermal cooling to temperatures below freezing. Such chambers are employed, among other uses, in observation of crystal growth in connection with aircraft flight experiments. Prior art chambers characteristically use a single wall construction for the access ports thereof which has caused thermal non-conformity in the walls, thereby resulting in uneven cooling of the chamber. Such prior art chambers have also been subject to fogging of the viewing window as the chamber cools.
Patents of possible interest in this general area include:
U.S. Pat. Nos. 4,242,589 (Sachs); 3,936,196 (Wickersheim); 3,966,297 (Vigreux et al); 3,899,243 (Haverkamp); and 4,372,652 (Pontefract).